Verified answer

May be this will help you:

• A: Assemblies

• B: Transducers / Sensors / Detectors

• C: Capacitors

• D: Storage devices

• E: Miscellaneous

• F: Fuses

• G: Generator, battery pack

• H: Indicators, signaling devices

• J: Connector / connector pin Joining another connector (P)

• K: Relays

• L: Inductors and filters

• M: Motors

• N: Analogue devices

• P: Measuring / test point / connector plug

• Q: Transistors

• R: Resistors

• S: Switches, push buttons, emergency stops and limit switches

• T: Transformers

• U: Integrated circuits, Power converters, DC power supplies

• V: Electron vacuum tubes tubes

• W: Wires, conductors, power, neutral and earthing busses

• X: Terminal strips, terminations, joins

• Y: Solenoids, electrical actuators

• Z: Filters

Hi JH, try

http://en.wikipedia.org/wiki/Reference_designator